Damaged buildings in the old city of Homs

International peace envoy Lakhdar Brahimi arrived in Syria's capital on Thursday as state forces pounded its eastern outskirts to flush out rebels trying to retain a foothold in Damascus.

Brahimi's mission is a challenging one as neither side in the rebellion against President Bashar al-Assad seems ready to put down arms. Nor does Brahimi enjoy the necessary support from divided world and Middle East powers.

Opposition activists reported a fighter jet flying overhead and helicopter gunships firing down on suburbs that have housed insurgents struggling to topple Assad after the ouster of four other Arab autocrats in popular revolts over the past 18 months, reports Reuters.

"There is a fresh campaign on the eastern parts of Damascus," said an activist, speaking on Skype from the capital. "Helicopters are roaming the skies and right now they are firing on Zamalka district."

The 17-month-old conflict is escalating, with more than 27,000 dead, and has engulfed many areas around the seat of government, once believed impregnable to Assad's opponents.

His forces appear to be trying to keep opposition fighters out of the heart of Damascus by bombarding rebel-infiltrated outskirts with tanks, artillery, and helicopters.

Brahimi, a veteran Algerian diplomat who replaced former U.N. Secretary General Kofi Annan as head of a struggling international peace mission on Syria, was expected to meet opposition figures and government officials, including Assad.

"There is a crisis, no one denies it," he said on arrival in the Syrian capital. "We hope to contribute to (ending the violence) during the days and weeks ahead."

But his mission suffers from the fact that Western powers, as well as Gulf Arab states, are backing the opposition, while Russia, Iran and China are supporting Assad's government. The result has been deadlock in the U.N. Security Council as the death toll climbs and the refugee count soars to over 200,000.

In Damascus, residents said the Free Syrian Army, a loose assortment of rebel forces, appeared to have pulled out of the southern neighbourhood of Tadamon. Troops were deployed across the district, according to a witness visiting the area.

Tadamon, which has seen heavy shelling and clashes in recent weeks, was partially destroyed. House after house stood in ruins, crumbling from bombardment or blackened by fire.